1. Field of the Invention
This invention relates to the field of compatibilized blends and composites of (a) thermoplastic copolymers of at least one alkenyl aromatic monomer and at least one alkenyl nitrile monomer and (b) copolymers of ethylene and at least one vinyl ester, and more particularly, to blends and composites of styrene-acrylonitrile copolymers and ethylene-vinyl acetate copolymers compatibilized by coreaction with a minor amount of an acid compatibilization agent.
2. Description of the Prior Art
It is well known in the art to produce high impact strength grades of alkenyl aromatic-alkenyl nitrile copolymers, particularly styrene-acrylonitrile (SAN) copolymers, by blending the copolymers with a nitrile rubber. Alternatively, the alkenyl aromatic and alkenyl nitrile monomers may be copolymerized in the presence of a polydiene rubber, usually a polybutadiene (PBD), to produce graft copolymers having particularly desirable properties of impact resistance, moldability, tensile strength and solvent resistance to alcohols and oils. Such compositions, of which the acrylonitrile-butadiene-styrene (ABS) copolymers are perhaps the best known representatives have poor properties of weather resistance, of heat aging resistance and of solvent resistance to ketones and aromatics.
Much effort has been expended to find a suitable substitute for the polydiene portion of ABS and similar copolymers. Among other candidates, rubbery ethylene-vinyl acetate (EVA) has been suggested, e.g., by Bartl and Hardt, Adv. Chem. Ser. No. 91, 477 (1969). However SAN does not suitably graft to EVA. Recent attempts to overcome this problem have included pre-exchanging some of the acetate groups of EVA for methacrylate groups thereby introducing graftable unsaturation therein (Japan Pat. No. 73-01,715), or by coreacting some 5-40% of a monoolefin in a modified grafting operation as described in U.S. Pat. No. 3,855,353. The latter technique requires the use of a solvent or large volumes of water and is limited to the use of EVA copolymers having a melt flow rate (MFR) in the range of from about 0.1 to 100, preferably from 3 to 5 under Condition E of ASTM D-1238. In the still more complex grafting procedure described in U.S. Pat. No. 3,742,090, SAN is grafted onto EVA which has been previously modified by the introduction of acrylic type unsaturation therein.
When a combination of components which normally are incompatible is desired, it is now known to achieve compatibilization by adding a preformed graft copolymer in which segments represent each of the incompatible components as in U.S. Pat. No. 3,485,777, or to react a mixture of such materials with a coupling agent, for example, a combination of an unsaturated carboxylic anhydride and a free radical initiator, to induce in situ grafting as in U.S. Pat. No. 3,645,939. Even these procedures have disadvantages: the process of the former patent requires special graft copolymer additives while that of the latter patent requires a volatile coupling agent which offers very low efficiency in practice.
In contrast to the complex processes previously described, my copending U.S. patent application Ser. No. 600,332, filed July 30, 1975, discloses and claims a simple, rapid and efficient process for the compatibilization of a variety of thermoplastic blends and composites by suitably mixing nitrile group-containing and nitrile-condensable functional group-containing components with a minor amount of an acid condensing agent. Compatibilized blends of SAN and EVA copolymers prepared in accordance with my aforesaid copending application demonstrated remarkable resistance to falling weight impact. However, it was found that the notched Izod impact resistance according to ASTM D-256 for unmodified polyalloys was lower than desirable, certain lower molecular weight components being required to induce suitable Izod impact strength.